Recently, with the increasing integration of IC chips, the space between the bumps of an IC chip is being narrowed to a finer pitch. Furthermore, the bump surface area is also being reduced. When bonding an IC chip to a circuit board, an anisotropic conductive film has widely used. However, since the lower limit of the particle size of the conductive particles is about 2 μm, it was difficult to use such an anisotropic conductive film for the bonding of a highly integrated IC chip and a circuit board. Furthermore, when a stud bump produced utilizing a bonding machine is used as a bump designed to handle a fine pitch and a smaller surface area, there is the drawback that the trapping of the conductive particles is low due to the bumps being formed into a roughly conical shape with the collapsing tips. Consequently, a technique is now used in which the bumps of the IC chip and the connection pads of the circuit board are directly bonded (NCF bonded) using an insulating adhesive, without the use of an anisotropic conductive film.
As an insulating adhesive used in such NCF bonding, conventionally, a thermosetting epoxy resin adhesive (Patent Document 1) has been used which exhibits a high cohesive force and which can ensure a high adhesion strength with respect to the adherend due to hydroxyl groups produced from a thermosetting reaction. However, although thermosetting epoxy resin adhesives have a good cohesive force and can ensure a good adhesion strength with respect to the adherend, their polymerization reaction temperature is a comparatively high 180 to 250° C. Moreover, since a thermosetting time of several hours is required, the IC chip can suffer damage during the thermosetting, and the bonding productivity is also low.
Accordingly, an attempt has been made to utilize an acrylic insulating adhesive that can undergo radical polymerization at a comparatively low temperature and in a short time in NCF bonding (Patent Document 2).